Machine and method for repairing rotor shafts



July 16, 1968 L. J. MOLINARO 3,392,610

MACHINE AND METHOD FOR REPAIRING ROTOR SHAFTS Filed June l 1964 2 Sheets-Sheet 1 wvama w July 16, 1968 J. MOLINARO 3,392,610

MACHINE AND METHOD FOR REPAIRING ROTOR SHAFTS Filed June 12, 1964 2 Sheets-Sheet 2 INVENTOR.

United States Patent 3,392,610 MACHINE AND METHOD FOR REPAIRING ROTOR SHAFTS Lawrence J. Molinaro, Silver Bay, Minn., assignor to Reserve Mining Company, Silver Bay, Minn., a corporation of Minnesota Filed June 12, 1964, Ser. No. 374,633 3 Claims. (Cl. 82-1) The invention relates to a novel and improved ap paratus for facilitating and expediting the servicing of extra large rotor-and-shaft assemblies such as are used in moving large volumes of air or other gases in certain metallurgical processes and elsewhere. In one such process with which applicant is familiar, namely the heat indurating of pellets made from taconite ore concentrates, the rotor or impeller blade or vane assembly can have a diametrical span of twelve feet and an axial Width of six feet, the rotor being fixed on a shaft almost two feet in diameter and about twenty-two feet long. As will appear of significance later herein such a rotor-and-shaft assembly weighs in excess of twenty tons and costs more than fifty thousand dollars. In operation the rotor is in effect a rotary pump, being installed in a suitably sized conduit where it feeds tremendous volumes of gas or air, sometimes at temperatures up to or above one thousand degrees Fahrenheit.

The customary manner of mounting the rotor wheel which carries the impelling vanes is to pin it on the central part of the shaft, and retain it in place by means of two rings or collars on the shaft, one on each side of the impeller hub. The collars are first highly heated so as to have a close but s'lidable fit on the cold shaft. They are advanced to abutment with the wheel hub and then cooled to tightly grip the shaft, this being conventionally known as a shrink fit.

When a fan wheel is assembled on a shaft and placed in service under wide temperature differentials, trouble is encountered from excessive vibrations arising from loosening of the retaining collars which expand in the higher temperature ranges thereby permitting the impeller wheel to become loose on the shaft. This causes surface damage in the shaft portions beneath the collars, and it is necessary to take the assembly out of service for repairs.

Repair procedure heretofore has involved shipping the entire rotor assembly, as a unit, back to the manufacturers shops where the shaft is cut from the wheel, the wheel hub is re-bored, and a new shaft is installed. This procedure is lengthy, operationally unsound, inconvenient, costly, and time consuming. Shafts of the size mentioned above are not standard items kept in stock, but have been manufactured to fit when needed. It has taken approximately two months to procure the billet stock and forge and machine a shaft. In shipping a large assembly of the dimensions set forth hereinabove, the railroads classify it as a high-wide load which is moved under restricted conditions and by daylight only. Slow transit time is added to the manufacturers delay in making repairs. The whole repair process, including loss of time and production interruption, greatly increases production costs.

An object of the present invention, therefore, is to devise means for readily, rapidly, and cheaply repairing rotor shafts for an assembly of the magnitude above indicated.

A further object of the invention is to devise means as defined in the last preceding paragraph which assures alignment accuracy during the shaft refinishing process.

A further object of the invention is to devise means as defined in the last two preceding paragraphs, by the use of which the expensive shaft can be salvaged and reused.

A further object of the invention is to devise means as defined in the last three preceding paragraphs, by the use of which complete repairs can be completed in a few days, instead of the replacement time of many weeks heretofore experienced.

A further object of the invention is to devise an apparatus for the reception and repair of a rotor shaft assembly of the magnitude above indicated whereby complete shaft repairs can be effected without removal of the rotor assembly from the apparatus.

Other objects and advantages will be apparent from a study of the present description of a preferred embodiment of the invention in conjunction with the accompanying drawings wherein FIG. 1 is a perspective view of a rotor and shaft assembly disposed on my repair rack, but without the cutting tool set-up.

FIG. 2 is a vertical sectional view taken transversely to the axis of the rotor shaft.

FIG. 3 is a fragmentary side elevational view showing a portion of the shaft and cutting tool set-up.

Referring now to the drawings, and for the time being to FIG. 1, the arrow 10 indicates a wheel or impeller having in this instance eight vanes 11 fixed on a hub 12 on a shaft 13. Plates 14 serve as braces or stiffeners between the vanes. Retaining collars 15 are shrunk on shaft 13 in tight abutment against the hub 12.

In FIG. 1 the rotor assembly, comprising the shaft 13 carrying the impeller wheel 10 and collars 15, is disposed on a repair rack built up from structural members including the longitudinal I-beams 17 and 18, the cross beams 19, 20, 21, 22, 23 and 24, and various upright or inclined columns 25, 26, 27, 28, 29, 30 and 31. These upright and inclined columns serve to support two end rails 32 and 33 which in turn carry the rotor assembly in the following manner.

A hearing pedestal 34 supports a shaft bearing beneath cap 35 and a bearing pedestal 36 supports a shaft bearing beneath cap 37. The pedestals or bearing blocks 34 and 36 are carried on the end rails 32 and 33. The shaft end extends through and beyond the bearing on block 34 and is further aligned by means shown as a lathe tail stock 38. The other end 13b of the shaft has keyed thereon a sprocket (not shown) driven by a chain within housing 39. A motor 40 through a gear reduction unit 41 drives a belt 42 which through suitable intermediate driving means drives the chain in housing 39.

By reason of the mechanical arrangement shown in FIG. 1 the rotor and shaft assembly can be removed as a unit from its conduit and lowered to rest on the blocks 34, 36. The same bearings are used in the repair rack of FIG. 1 as are used on the shaft in its Working position. Actually the same bearing caps 35, 37 are transferred to the repair rack and are secured by bolts 45. As will appear, when the shaft is being refinished it is being done while aligned in the same identical bearings as will be used in service, making it possible to achieve a high degree of accuracy in re-aligning the shaft when putting it back in service.

On each side of the wheel 10' there is a portion 13c of the shaft 13 which is slightly raised (FIG. 3) and which receives the collar 15. Beneath the shaft on each side of the wheel I dispose a finishing tool and means for holding and positionally adjusting such tool. In the present instance such means includes a conventional milling machine bed 46 (FIG. 2) which carries tool holding means 47 and a cutting tool 48. A grinding tool or polishing means can readily be substituted. The machine bed has a longitudinal feed 49, a cross feed 50, and a vertical adjustment 51 as will be familiar to those skilled in the mechanic'al arts.

Assuming that a shaft assembly needs service it is removed from its conduit. The collars 15 are loose, as hereinbefore described, resulting from thermal differentials in service, and are readily removed from the portion 13c of the shaft. The shaft assembly including its end bearings is then positioned on the repair rack so that the driven end 13b of the shaft is in mesh with its driving gear or sprocket (not shown) and the bearings are supported on hearing blocks or pedestals 34, 36. The caps 35, 37 are bolted down and the tail stock 38 is centered on the shaft end 13a. The rotor assembly is then ready to be rotated at any suitable speed for cutting, grinding, or polishing.

I have shown only in bare essentials the tool supporting bed 46 which is carried on a column 52 for vertical movement. I have used, for example, a commercially available milling machine bed and support with all upper turret mechanism removed from column 52 to afford clearance under shaft 13.

Only the shaft portions 130 beneath and immediately adjacent collars 15 actually require refinishing as indicated on FIG. 3. These portions 13c are machined and ground to a suitable diameter to remove all traces of damage and to receive the new collars, although in some instances I machine and polish all exposed portions of shaft 13 to retain the step fit. With the arrangement as shown, and herein described, I have found it possible to attain a dimensional accuracy of 0.0005 inch by machining, and a further accuracy of 50 micro-inches (0.00005) by finish grinding and polishing. In FIG. 3 the depth of cut being taken is exaggerated.

The use of a standard milling machine bed affords threedimensional positional adjustment of the finishing tools, namely vertical, longitudinal, and cross feeds. Other machining apparatus set-ups can be used which provide suitable tool adjustments.

After the shaft portions 130 are refinished new collars 15 are provided, the shaft assembly is lifted from the rack, the collars are heated to slip over the shaft and over portions 13c, and are then cooled to a tight shrink fit and pinned. The rotor assembly is then returned to its place of normal use in the conduit.

I claim:

1. A machine for repairing a rotor shaft having bearings thereon spaced apart a predetermined distance and having at an intermediate point thereon an impeller wheel and having collar-receiving portions disposed immediately adjacent to and on each side of said impeller Wheel upon which wheel retaining collars are fixedly disposed in service, said machine comprising a base, bearing support means at each end of the base spaced apart said predetermined distance and suitably dimensioned and shaped to respectively receive the bearing in which said shaft operates, two shaft finishing means spaced longitudinally to receive said impeller wheel between them and carried on said base one beneath each said collar-receiving shaft portions, means for bringing each said finishing means to finishing relationship with its associated collar-receiving shaft portion, and means for rotating said rotor-shaft assembly at a speed suitable for the finishing operation.

2. A machine for repairing rotor shafts of predetermined length between end bearings and requiring refinishing of diameters intermediate the ends thereof, comrising a base, horizontal end rails on said base at opposite ends thereof having the same spacing between them as the end bearings of a shaft, means on each end rail specially shaped for receiving and supporting the Working end bearings of a shaft, shaft rotating means on said base, and shaft finishing means on said base in position to engage said shaft diameters intermediate the shaft ends when a shaft is supported by said bearings on said end rails, said finishing means positioned to clear said shaft and parts thereon as said shaft is lowered into said bearings.

3. The method of refinishing shaft diameters intermediate the ends of a shaft having a predetermined length between bearings, comprising providing repair means having means for supporting shaft bearings at said predetermined spacing, said repair means having shaft refinishing means between said shaft bearing support means, removing said shaft from its bearings, placing said bearings in said bearing support means, securing said shaft in said bearings, rotating said shaft, and operating said shaft refinishing means in engagement with said shaft.

References Cited UNITED STATES PATENTS 972,297 10/ 1910 Tyberg 822 2,140,565 12/ 1938 Swenson 82-2 3,200,679 8/ 1965 Johnson 82-8 X FOREIGN PATENTS 20,534 Great Britain.

LEONIDAS VLACHOS, Primary Examiner. 

3. THE METHOD OF REFINISHING SHAFT DIAMETERS INTERMEDIATE THE ENDS OF A SHAFT HAVING A PREDETERMINED LENGTH BETWEEN BEARINGS, COMPRISING PROVIDING REPAIR MEANS HAVING MEANS FOR SUPPORTING SHAFT BEARINGS AT SAID PREDETERMINED SPACING, SAID REPAIR MEANS HAVING SHAFT REFINISHING MEANS BETWEEN SAID SHAFT BEARING SUPPORT MEANS, REMOVING SAID SHAFT FROM ITS BEARINGS, PLACING SAID BEARINGS IN SAID BEARING SUPPORT MEANS, SECURING SAID SHAFT IN SAID BEARINGS, ROTATING SAID SHAFT, AND OPERATING SAID SHAFT REFINISHING MEANS IN ENGAGEMENT WITH SAID SHAFT. 